Mj. Vepraskas et al., POROSITY FACTORS THAT CONTROL THE HYDRAULIC CONDUCTIVITY OF SOIL-SAPROLITE TRANSITIONAL ZONES, Soil Science Society of America journal, 60(1), 1996, pp. 192-199
Slowly permeable transitional horizons separate soil and saprolite, bu
t these horizons cannot be identified easily in the field. The objecti
ves of this study were to determine why the soil-saprolite transitiona
l zone (BC and CB horizons) is slowly permeable, and to evaluate ways
for identifying it in the field, Two saprolite deposits were studied i
n the North Carolina Piedmont. At each site, saturated and unsaturated
hydraulic conductivities (K-sat and K-unsat) were measured for major
horizons. Volume fractions of water-conducting pores were also compare
d with the changes in hydraulic conductivity with depth. Horizon mean
K-sat values at both sites ranged from virtually 0 to approximately 3
cm h(-1). The lowest K-sat values (<0.3 cm h(-1)) occurred in or near
the transitional horizons that were directly below the Bt horizons. Ch
anges in the volume of pores within or between mineral grains (termed
inter/intraparticle pores) with depth corresponded to changes in both
K-sat and K-unsat. In the transitional horizons, the inter/intrapartic
le pores were plugged with clay and this caused the horizons to have l
ow K values. In situ measurements of K-sat with depth were the most ac
curate technique to use for identifying transitional zones in the fiel
d. Examination of both the soil and rock structures in pits was also a
n acceptable technique. Texture and consistence were not considered re
liable for pin-pointing transitional horizons.